Backlink analysis service Majestic SEO was proclaimed the most advanced backlink analysis tool by Ann Smarty, in-house SEO expert at Search Engine Journal.
Majestic SEO tracks the number of sites linking back to your own. It gleans its figures from two sources of data: its own web crawl (32,690,802,864 sites have been crawled so far, including 211,051,271,656 unique URLs), and backlinks reported by Google and Yahoo.
A panoply of reports are also available, including domain overview data, anchor text data and daily domain updates.
The tool is free once marketers request a report for their own sites (ownership must be verified). Reports can also be drawn for competitors' sites — but users must purchase credits in order to see them. Other merits are described at Search Engine Journal (linked above).
